Does the abnormal pattern of breathing in patients with interstitial lung disease persist in deep, non-rapid eye movement sleep

Patients with interstitial lung disease (ILD) characteristically exhibit an increased ventilation and breathing frequency when awake. We wanted to see if these increases persisted during deep non-REM sleep. Using noninvasive techniques, we have quantified the pattern of breathing, arterial oxygen satuation, and transcutaneous PCO₂ (Ptc(CO₂)) during standardized conditions of relaxed wakefulness and during Stage 4 (S4) sleep in eight patients with ILD and eight age-matched normal control subjects. The patients were given supplemental oxygen in order to prevent hypoxic ventilatory stimulation. The data were compared between the two groups during each of these states and also between states within each group. During wakefulness in the patients, respiratory frequency (f) and Ptc(CO₂) were higher (p < 0.001 and p < 0.05, respectively) and inspiratory time (TI) and expiratory time (TE) were shorter (p < 0.05 and p < 0.001, respectively) than in the normal subjects. However, during S4 sleep, there were no significant differences between groups. Comparing wakefulness with S4 sleep: in the normal subjects during sleep, f and Ptc(CO₂) were increased (p < 0.01 and p < 0.05, respectively), TE was shortened (p < 0.01), and ventilation (V̇I) was unchanged. In contrast, in the patients, f decreased (p < 0.001), TE lengthened (p < 0.01), V̇I decreased (p < 0.05), and the rise in Ptc(CO₂) seen in the normal subjects during sleep did not occur. We have considered various explanations for these observations, including the possibility that the increased drive to breathe in patients with ILD during wakefulness may be a behavioral phenomenon, dependent upon cortical perception of afferent information from the respiratory apparatus, which disappears during non-REM sleep.